title: Surface charges of the membrane crucially affect regulation of Na,K-ATPase by phospholemman (FXYD1).
abstract: The human α1/His10-β1 isoform of Na,K-ATPase has been reconstituted as a complex with and without FXYD1 into proteoliposomes of various lipid compositions in order to study the effect of the regulatory subunit on the half-saturating Na⁺ concentration (K(½)) of Na⁺ ions for activation of the ion pump. It has been shown that the fraction of negatively charged lipid in the bilayer crucially affects the regulatory properties. At low concentrations of the negatively charged lipid DOPS (<10 %), FXYD1 increases K(½) of Na⁺ ions for activation of the ion pump. Phosphorylation of FXYD1 by protein kinase A at Ser68 abrogates this effect. Conversely, for proteoliposomes made with high concentrations of DOPS (>10 %), little or no effect of FXYD1 on the K(½) of Na⁺ ions is observed. Depending on ionic strength and lipid composition of the proteoliposomes, FXYD1 can alter the K(½) of Na⁺ ions by up to twofold. We propose possible molecular mechanisms to explain the regulatory effects of FXYD1 and the influence of charged lipid and protein phosphorylation. In particular, the positively charged C-terminal helix of FXYD1 appears to be highly mobile and may interact with the cytoplasmic N domain of the α-subunit, the interaction being strongly affected by phosphorylation at Ser68 and the surface charge of the membrane.
authors.affiliation: Department of Biology and Graduate School of Chemical Biology, University of Konstanz, 78464, Constance, Germany.
authors.forename: Erica
authors.initials: E
authors.lastname: Cirri
authors.forename: Corinna
authors.initials: C
authors.lastname: Kirchner
authors.forename: Simon
authors.initials: S
authors.lastname: Becker
authors.forename: Adriana
authors.initials: A
authors.lastname: Katz
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Karlish
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Apell
mesh_terms: D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006801:Humans; D007477:Ions / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D007700:Kinetics; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D009994:Osmolar Concentration; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D011510:Proteolipids / Q000378:metabolism; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D007477:Ions; D008563:Membrane Lipids; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D020033:Protein Isoforms; D011510:Proteolipids; C020485:proteoliposomes; C069141:phospholemman; D017868:Cyclic AMP-Dependent Protein Kinases; D000254:Sodium-Potassium-Exchanging ATPase